Show that the power of the achromatic combination of two convex lenses of the same material is equal to the mean power of the lenses.

An achromatic combination of lenses is to be made by using a convex and a concave lens. The two lenses should have

Show that in order to obtain a converging achromatic combination the dispersive power of the material of the concave lens must be greater than that of the material of the convex lens.

Can two lenses of the same material produce achromatism when placed in contact? Explain.

It is desired to make an achromatic combination of two lenses, (L_(1)& L_(2)) made of materials having dispersive power omega_(1) and omega_(2)(ltomega_(1)) . If the combination of lenses is converging then:

Two thin lenses, when in contact, produce a combination of power +10 dioptres. When they are 0.25m apart, the power is reduced to +6 dioptres. The power of the lenses in dioptres, are

Power (P) of a lens is given by reciprocal of focal length (f) of the lens. i.e. P = 1//f . When f is in metre, P is in dioptre. For a convex lens, power is positive and for a concave lens, power is negative. When a number of thin lenses of powers p_(1), p_(2), p_(3).... are held in contact with one another, the power of the combination is given by algebraic sum of the powers of all the lenses i.e., P = p_(1) + p_(2) + p_(3) + ........ Answer the following questions : Two thin lenses are in contact and the focal length of the combination is 80 cm . If the focal length of one lens is 20 cm , the focal length of the other would be

When curved surface of a plane convex lens is silvered then the focal power of the lense is